An angle portion is situated at peripheral edge of anterior chamber of an eyeball and of which abnormalities such as too wide or too narrow angle, open or closure angle and adhesion are related to intraocular pressure, occurrence of glaucoma or the like. In ophthalmology, therefore, examination on such angle portion is prevailing.
Since direct observation on an angle portion is difficult, it has hitherto been a usual practice to use a contact lens for gonioscopy as disclosed in Japanese Examined Patent Publication No. 13039/1974. However, when there is a closure or adhesion in the angle portion of a subject, even such a contact lens cannot allow observation on the inner part of the angle portion.
Therefore, usually, the angle portion of a subject is firstly observed using a contact lens for gonioscopy, and then, if closure or adhesion is found in the angle portion, an indentation gonioscopy 4 provided therein with a lens 2 as shown in FIGS. 7 and 8 is used to further observe the angle portion. A tip face 6 of the indentation gonioscopy 4 is brought into contact with the cornea of the subject and made to press it so as to enlarge the angle portion thereby allowing observation thereon.
With such a conventional technique, however, the observation work has been troublesome while at the same time inflicting much pain on a subject because the contact lens for gonioscopy should be changed with the indentation gonioscopy as required.
Further, an indentation gonioscopy of the conventional type is adapted to press a part of cornea periphery so as to enlarge a part of angle portion on the opposite side of the pressed part thereby allowing observation. Hence, it is likely that there is produced local strain or wrinkle in the cornea during the pressing operation, thus making observation unclear. Accordingly, the conventional gonioscope has involved a problem of difficulty in observation.
In addition, such an indentation gonioscopy is likely to slip on a subject eye upon pressing it; hence, it is very difficult to continuously press the target pressing position of cornea of an eyeball for observation. Accordingly, the conventional indentation gonioscopy has involved another problem of requiring a high technique and skill for observation.
The present invention has been made with the background of the foregoing circumstances. Thus, it is an object of the present invention to provide a contact lens for intraocular observation of very good operability, with which, besides observation on a subject eye in a normal state, observation can be made on the inner part of an angle portion as required if there is a closure or adhesion, while at the same time generation of strain or wrinkle in the cornea of a subject eye during observation can be advantageously avoided and a slip on the subject eye can be effectively prevented.